1. Field of the Invention
This invention relates to a displacement type ear microphone and a method for the manufacture thereof, and more particularly to a displacement type ear microphone sensing bone vibration having an electroacoustic transducer element thereof rendered hard to break.
2. Description of the Prior Art
First the conventional displacement type vocal bone vibration ear microphone will be described with reference to FIG. 1 and FIG. 2.
FIG. 1 is a perspective view illustrating an appearance of the conventional displacement type vocal bone vibration ear microphone. FIG. 2 is a perspective view illustrating an appearance of the microphone of FIG. 1 after removal of a damper member thereof.
As illustrated in FIG. 2, a bar-shaped or ribbon-shaped electroacoustic transducer element 2 such as a bimorph cell of barium titanate ceramic, for example, is planted in a support member 1. To the support member 1 side end of the electroacoustic transducer element 2 is electrically connected a lead wire 3. This lead wire 3 is extended through the support member 1 and led out of the microphone.
Around the bar-shaped or ribbon-shaped electroacoustic element 2, a cylindrical damper member 4 formed of silicone mold or other rubbery substance is disposed as illustrated in FIG. 1. This damper member 4 is produced so that the circular cross section perpendicular to the axis thereof is virtually equal to or slightly smaller than the diameter of the auditory meatus (the auditory canal). Thus, the damper member 4 suits insertion in the auditory meatus.
In the displacement type vocal bone vibration ear microphone constructed as described above, when the microphone is inserted in the auditory meatus, the bone vibration transmitted to the auditory meatus flexes the damper member 4 and consequently flexes the electroacoustic transducer element 2 as well. By the electroacoustic transducer element 2, this bone vibration is converted into an electrical signal. The electric signal is forwarded through the lead wire 3 to a device of subsequent step (not shown) connected thereto.
The conventional displacement type vocal bone vibration ear microphone has an advantage that it satisfactorily picks up only the bone vibration, perfectly avoids picking up the aerial vibration such as noise, and sparingly induces howling. It nevertheless entails a disadvantage that since the electroacoustic transducer element is mechanically fragile, it must be handled with the greatest possible care lest it should be exposed to unwanted external force.
The inventor, therefore, has experimentally manufactured a displacement type bone vibration ear microphone constructed to have an electroacoustic transducer element thereof rendered hard to break as illustrated in FIG. 3.
In this microphone, three inflexible piano wires 5a, 5b, and 5c are planted on a support member 1 at three points around an electroacoustic transducer element 2 and a damper member 4 is molded of silicone resin to enclose the piano wires.
In this microphone, the damper member 4 is not flexed even when it is exposed to any unwanted external force because it is reinforced with the three piano wires 5a, 5b, and 5c. As the result, the electroacoustic transducer element 2 is not flexed by such an external force and is prevented from breakage.
In the displacement type bone vibration ear microphone of this construction, however, the piano wires are not effectively utilized as an auxiliary vibrator for the electroacoustic transducer element because the piano wires are too rigid to flex and further because the piano wires are separated from the electroacoustic transducer element. This microphone, therefore, suffers from a disadvantage that it has poor sensitivity in picking up the bone vibration.